Recycling method

ABSTRACT

A plastic container has a diamond like carbon film  20   b  formed on the inner surface of the container  20  made of plastic material  20   a . The thickness of the diamond like carbon film  20   b  is within a range from 0.05 to 5 μm. The container  20  coated with the diamond like carbon film can be used for a returnable bottle for beverage.

TECHNICAL FIELD

This invention relates to a plastic container, the inner surface ofwhich is coated with a hard carbon film.

BACKGROUND ART

In general, plastic containers are widely used as packaging materials invarious kinds of fields such as a food field and a medicine fieldbecause plastic containers have various benefits which are easy to mold,light in weight and low in cost. However, as is well known, plasticpermits low molecular gas, such as oxygen and carbon dioxide, topermeate therethrough, and furthermore, plastic sorbs (i.e., both ofabsorption and adsorption occur simultaneously) inside therein lowmolecular organic compound, namely, low molecular organic compoundinfiltrates into the plastic composition and diffuses therein in such amanner that the low molecular organic compound is absorbed inside theplastic. Therefore, plastic containers are restricted in many aspects tospecific objects and forms in use in comparison with other containerssuch as a glass container.

For example, in case that a carbonated beverage such as beer is filledinto a plastic container, oxygen in the atmosphere permeates the wall ofthe plastic container to reach inside the plastic container, thusgradually oxidizing and deteriorating the beverage contained therein. Inaddition, carbon dioxide gas in the carbonated beverage permeates, inreverse, the wall of the plastic container and is released off towardoutside, thus the carbonated beverage loses its savor.

Further, in case that beverages having aroma component such as orangejuice are filled into a plastic container, aroma component (such aslimonene in the case of the orange juice) which is a low molecularorganic compound is sorbed inside the plastic. Consequently, chemicalcomposition of the aroma components in the beverages may lose itsbalance to deteriorate the beverages in quality.

In addition, a plastic container may have a problem that low molecularcompound contained in the plastic container dissolves in a liquidcontent contained in the container. More specifically, in case thatcontent (especially, liquid) requiring a high purity is filled into thecontainer, plasticizer, residual monomer or other additives dissolvesout of the container into the liquid content, thus deteriorating purityof the content.

Furthermore, at present, how large numbers of used containers are to betreated has become a social issue, and collecting the used containersfor the sake of recycling resources is in progress. However, when a usedplastic container is to be used as a recycled container, if the usedplastic container is left in the environment before being collected,various low molecular organic compounds, such as those producing moldodor, are sorbed in the plastic container, something that does nothappen with glass containers. The low molecular organic compounds thussorbed in the plastic container remain in the plastic even after thecontainer is washed. The sorbed low molecular organic compoundsgradually dissolve out of the plastic into the contents of the plasticcontainer as impurities, thereby deteriorating the contents in qualityand causing a hygienic problem. As a result, plastic containers can behardly used as returnable containers, namely, containers collected to bereused.

In order to suppress the above-mentioned features of the plastic,namely, the feature of permitting low molecular gas to permeatetherethrough or the feature of sorbing low molecular organic compoundtherein, crystals in the plastic have been oriented to enhancecrystallinity or thin sheets of plastic having a lower sorption or thinfilms of aluminum have been laminated. In either methods, however,problems of gas barrier property and the sorption of low molecularorganic compound cannot be perfectly solved while maintaining the basicproperties of the plastic container.

Recently, there has appeared a thin film forming technology for a DLC(Diamond like carbon) film and it is known that laboratory tools such asbeakers and flasks are coated with the DLC film. The DLC film comprisesamorphous carbon including mainly SP³ bond between carbons. The DLC filmis a hard carbon film which is very hard, and has a good insulation, ahigh index of refraction and a smooth morphology.

Japanese Patent Provisional Publication No. 2-70059 discloses an examplein which the DLC film forming technology is applied to laboratory toolsfor coating thereof. An apparatus for forming the DLC film disclosed inthe above publication comprises the followings. As shown in FIG. 16, acathode 2 is disposed in a reaction chamber 1 having an inlet 1A forcarbon resource gas which generates carbon or is converted to carbon andan outlet 1B, and a laboratory tool 3 such as a beaker is accommodatedin a space 2A formed in the cathode 2. The reaction chamber 1 isdecompressed by discharging air from the outlet 1B after an earthedanode 4 is inserted into an inner space of the laboratory tool 3. Afterthe carbon resource gas is led into the reaction chamber 1 from theinlet 1A, a high frequency is impressed on the cathode 2 from a highfrequency power source 5 to excite the carbon resource gas, thusgenerating plasma to form the DLC film on the surfaces of the laboratorytool 3.

However, in the above DLC film forming apparatus, the reaction chamber 1accommodates the cathode 2 and the anode 4, so that the volume of thereaction chamber 1 is remarkably large in comparison with that of thelaboratory tool 3 to be coated. Therefore, it causes wastes of time andenergy for a vacuum operation of the reaction chamber. Furthermore,since the film forming speed (rate) in the above DLC film formingapparatus is 10 to 1000 Å per minute, which speed is slow, there is aproblem in which it is difficult to continuously form the film at a lowcost.

The conventional DLC film forming apparatus described above is appliedto laboratory tools such as beakers and flasks so as to mainly furtherincrease their qualities, so that the manufacturing cost and timethereof is not much considered. However, containers used for beveragessuch as beer and orange juice must be manufactured in large quantitiesat low cost. Accordingly, the DLC film forming apparatus cannot beapplied to the containers used for beverages.

In the above DLC film forming apparatus, since the carbon resource gasmoves into the space between the inner surface of the cathode 2 and theouter surface of the laboratory tool 3 to be coated, it is impossible tocoat only the inner surface of the laboratory tool 3.

Containers for beverages often collide with each other during themanufacturing process in a factory or during the selling process in astore, unlike a laboratory tool such as a beaker or a flask. When a DLCfilm is formed on the outer surface of a container for beverages, theDLC film itself is damaged by the collisions to decrease the value ofmerchandise in the containers. Accordingly, it is required that the DLCfilm is formed only on the inner surface of a container.

It is an object of this invention to provide a plastic container coatedwith carbon film which can solve the problems of gas barrier propertyand sorption inherently owned by the plastic while maintaining basicproperties of plastic, which can be returnably used to extend the fieldsand the forms in which plastic containers can be used, which can becontinuously manufactured at a low cost, and which is not damaged duringhandling of the containers.

DISCLOSURE OF INVENTION

In order to attain the above object, a plastic container of thisinvention comprises a bottle for beverages made of a plastic materialwith a hard carbon film formed only on an inner surface thereof. Inaddition, the hard carbon film comprises a diamond like carbon film.

According to the above plastic container of the invention, permeabilityof the container against low molecular inorganic gas such as oxygen andcarbon dioxide can be remarkably lowered, and furthermore, the sorptionin the plastic of various low molecular organic compounds having a smellcan be completely suppressed. The formation of the hard carbon film doesnot deteriorate the transparency of the plastic container.

The hard carbon film preferably comprises a diamond like carbon film.The diamond like carbon film is a kind of hard carbon film which iscalled i-carbon film or hydrogenated amorphous carbon film, and isamorphous carbon film mainly including SP³ bond.

Furthermore, the thickness of the diamond like carbon film is preferablywithin a range of 0.05-5 μm. With the thickness of the diamond likecarbon film limited to the above range, adhesive property of the film toplastic material, the durability and transparency and the like of thecontainer can be obtained, and in addition, the sorption in the plasticof low molecular organic compound can be effectively suppressed and gasbarrier property of the container can be improved.

The following resins are used as plastic material for containers.Polyethylene resin, polypropylene resin, polystyrene resin, cycloolefinecopolymer resin, polyethylene terephthalate resin, polyethylenenaphthalate resin, ethylene-(vinyl alcohol) copolymer rein,poly-4-methyl pentene-1 resin, poly (methyl methacrylate) resin,acrylonitrile resin, polyvinyl chloride resin, polyvinylidene chlorideresin, styrene-acrylonitrile resin, acrylonitrile-butadien-styreneresin, polyamide resin, polyamideimide resin, polyacetal resin,polycarbonate resin, polybutylene terephthalate resin, ionomer resin,polysulfone resin and polytetra fluoroethylene resin.

Furthermore, the thickness of the diamond like carbon film is preferablywithin a range of 0.05-5 μm. With the thickness of the diamond likecarbon film limited to the above range, adhesive property of the film toplastic material, the durability and transparency and the like of thecontainer can be obtained, and in addition, the sorption in the plasticof low molecular organic compound can be effectively suppressed and gasbarrier property of the container can be improved.

The following resins are used as plastic material for containers.Polyethylene resin, polypropylene resin, polystyrene resin, cycloolefinecopolymer resin, polyethylene terephthalate resin, polyethylenenaphthalate resin, ethylene-(vinyl alcohol) copolymer resin,poly-4-methyl pentene-1 resin, poly (methyl, methacrylate) resin,acrylonitrile resin, polyvinyl chloride resin, polyvinylidene chlorideresin, styrene-acrylonitrile resin, acrylonitrile-butadien-styreneresin, polyamide resin, polyamideimide resin, polyacetal resin,polycarbonate resin, polybutylene terephthalate resin, ionomer resin,polysulfone resin and polytetra fluoroethylene resin.

When the plastic container with a hard carbon film formed on an innersurface thereof is applied to a bottle for beverages, the plasticcontainer can be returnably used in place of a conventional glasscontainer.

As described above, the plastic container coated with a hard carbon filmof the invention has an excellent gas barrier property and cancompletely suppress the sorption in the plastic of low molecular organiccompound such as odor component, thus making it possible that thecontainer is extensively used as a packaging container in various manyfields and as a returnable container capable of refilling therein.Furthermore, since the hard carbon film is formed only on the innersurface of the container in the invention, there is no concern over thedamage of the formed hard carbon film during handling of the container.

In case that the hard carbon film formed on the inner surface of thecontainer comprises a diamond like carbon film, the above-mentionedeffects become more remarkable.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinally sectional view showing an embodiment of amanufacturing apparatus for manufacturing a plastic container coatedwith carbon film according to this invention;

FIG. 2 is a partially enlarged sectional view of the above embodiment;

FIG. 3 is a plan view of an insulating plate of the above embodiment;

FIG. 4 is a longitudinally sectional view showing an embodiment of aplastic container coated with carbon film according to this invention;

FIG. 5 is a table showing conditions for forming hard carbon film;

FIG. 6 is a table showing results evaluating thickness of film and thelike of hard carbon film formed under the conditions shown in FIG. 5;

FIG. 7 is a table showing results evaluating oxygen permeability and thelike of the hard carbon film formed under the conditions shown in FIG.5;

FIG. 8 is a graph showing transmitted light spectrum in the ultravioletand visible region of the plastic container with the hard carbon filmformed thereon under the conditions shown in FIG. 5;

FIG. 9 is a graph showing Raman spectrum of the hard carbon film formedunder the conditions shown in FIG. 5;

FIG. 10 is a table showing other conditions for forming the hard carbonfilm;

FIG. 11 is a table showing results evaluating thickness and the like ofhard carbon film formed under the conditions shown in FIG. 10;

FIG. 12 is a table showing results evaluating oxygen permeability andthe like of the hard carbon film under the conditions shown in FIG. 10;

FIG. 13 is a table showing further other conditions for forming the hardcarbon film;

FIG. 14 is a table showing results evaluating thickness and the like ofthe hard carbon film formed under the conditions shown in FIG. 13;

FIG. 15 is a table showing results evaluating permeability and the likeof the hard carbon film formed under the conditions shown in FIG. 13;and

FIG. 16 is a longitudinally sectional view showing a prior art.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the invention is explained with reference to drawings.

FIG. 1 shows a manufacturing apparatus for manufacturing a plasticcontainer coated with carbon film according to the invention. Themanufacturing apparatus has a ceramic insulating plate 11 fixed on abase 10, on which insulating plate an external electrode 12 is mounted.The external electrode 12 itself serves at the same time as a vacuumchamber for forming a DLC film, inside of which external electrode aspace is formed for accommodating a container 20 to be coated. The spaceformed in the external electrode 12 is slightly larger than thecontainer 20 accommodated therein. In this embodiment, the container 20is a bottle for beverage, however, the container may be used for otherobjects.

The external electrode 12 comprises a main body 12A and a cover 12Bprovided detachably on the main body 12A so as to tightly close theinterior of the main body 12A. A high frequency power source 14 isconnected to the lower portion of the external electrode 12 through amatching device 13 and connecting members 30, 30 provided on the base10. Furthermore, a discharging pipe 15 is communicated as shown in FIG.1 with the space formed in the external electrode 12 so as to dischargeair in the space by a vacuum pump not shown.

An internal electrode 16 is inserted into the space of the externalelectrode 12 so as to be disposed at the center portion of the space.The discharging pipe 15 terminates at the upper surface of the base 10so as to be opened to a circular space 11B formed at the center portionof the insulating plate 11. The internal electrode 16 is so formed thatthe electrode 16 can be inserted into the container 20 through the mouth20A of the container 20, and the external shape of the internalelectrode 16 is approximately similar figures to the internal shape ofthe container 20. It is preferable that the distance between theexternal electrode 12 and the internal electrode 16 is keptapproximately even at every position of the container 20 within therange of 10-150 mm.

A feed pipe 17 for feeding raw gas is connected with the internalelectrode 16. A raw gas is fed through a gas flow rate controller (notshown) from the feed pipe 17 for feeding raw gas into the internalelectrode 16. The raw gas thus fed into the internal electrode 16 blowsoff from a plurality of blowing openings 16A formed on the internalelectrode 16. A plurality of blowing openings are preferably formed onthe side portion of the internal electrode 16 as shown in FIG. 1 inorder to evenly diffuse the blown raw gas. However, in case that the rawgas is evenly diffused immediately after being blown off from theinternal electrode 16, one blowing opening may be formed on the top ofthe internal electrode 16. The internal electrode 16 is earthed throughthe feed pipe 17 for the raw gas.

The insulating plate 11 comprises a short cylindrical body having anouter circumferential surface and an inner circumferential surface, andhas a plurality of grooves 11A (four grooves in this embodiment) asenlargedly shown in FIGS. 2 and 3. Each of the grooves 11A is disposedat an angular interval of 90° and the bottom surface of each groove 11Ais slanted downwardly from an abutting point P (FIG. 2) to the innercircumferential surface of the insulating plate 11, at which abuttingpoint an inner circumferential surface of the external electrode 12 isabutted on the insulating plate 11. As shown in FIG. 2, an externalspace 21A formed between the inner surface of the external electrode 12and the outer surface of the container 20 is communicated with thedischarging pipe 15 through the grooves 11A in a state wherein thecontainer 20 is accommodated in the external electrode 12 with the mouth20A of the container 20 abutted against the insulating plate 11.

Then, a method for forming a DLC film by the above manufacturingapparatus is explained.

The plastic container 20 is inserted from the upper opening of the mainbody 12A into the external electrode 12 with the cover 12B detached fromthe main body 12A. At this time, the internal electrode 16 is insertedinto the container 20 through the mouth 20A of the container 20. Then,the mouth 20A is abutted against the insulating plate 11 in such mannerthat the plastic container 20 is placed in an appropriate position inthe external electrode 12, and the cover 12B then closes the upperopening of the main body 12A so that the external electrode 12 istightly sealed. At this time, the distance between the inner surface ofthe external electrode 12 and the outer surface of the container 20 ismaintained approximately even while the distance between the innersurface of the container 20 and the outer surface of the internalelectrode 16 is maintained approximately even.

Thereafter, air in the external electrode 12 is discharged through thedischarging pipe 15 by a vacuum pump so that the inside of the externalelectrode 12 becomes vacuum. More specifically, the internal space 21Bas well as the external space 21A between the outer surface of thecontainer 20 and the inner surface of the external electrode 12 becomesvacuum by means of the grooves 11A formed in the insulating plate 11.This is because unless the external space 21A is vacuum, the temperaturein the external space 21A becomes remarkably high upon generatingplasma, thus affecting the plastic material of the container 20.

The degree of vacuum is preferably within a range from 10⁻² to 10⁻⁵torr. With a lower degree of vacuum of over 10⁻² torr, impurities in thecontainer are much increased, on the other hand, with a higher degree ofvacuum under 10⁻⁵ torr, a long time and a large energy are needed todischarge the air in the container 20.

Then, the raw gas as carbon resource is supplied to the feed pipe 17through the gas flow rate controller not shown in the drawing, and thenthus supplied raw gas is blown off through the blow openings 16A intothe internal space 21B in the state of vacuum between the outer surfaceof the internal electrode 16 and the inner surface of the container 20.The flow rate of the raw gas is preferably within a range from 1 to 100ml/min, by which flow rate of the raw gas the pressure in the internalspace 21B is adjusted within the range from 0.5 to 0.001 torr.

Since the air in the external space 21A is discharged through thegrooves 11A, the pressure in the external space 21A becomes lowerslightly later than the pressure in the internal space 21B becomeslower. Therefore, when the discharge of the air is just started, thepressure in the external space 21A is slightly higher than the pressurein the internal space 21B. Accordingly, in the case that the supply ofthe raw gas get started immediately after the discharge of the air inthe container is over, the raw gas blown into the internal space 21Bdoes not get into the external space 21A.

Aliphatic hydrocarbons, aromatic hydrocarbons, oxygen containinghydrocarbons, nitrogen containing hydrocarbons, etc., in gaseous orliquid state at a room temperature are used as the raw gas. Especially,benzene, toluene, o-xylene, m-xylene, p-xylene and cyclohexane eachhaving six or more than six carbons are preferable. These raw gases maybe used per se, however, mixture of two or more than two kinds of rawgases may be used. Furthermore, these gases may be used in the state ofdilution with inert gas such as argon and helium.

After the supply of the raw gas into the container, electric power isimpressed to the external electrode 12, via the matching device 13, fromthe high frequency electric source 14. The impression of the electricpower generates plasma between the external electrode 12 and internalelectrode 16. At this moment, the internal electrode 16 is earthed,however, the external electrode 12 is insulated by the insulating plate11. Therefore, negative self-bias is generated at the external electrode12. This causes a DLC film to be uniformly formed on the inner surfaceof the container 20.

More specifically, the formation of the DLC film on the inner surface ofthe container 20 is performed by means of an improved plasma CVD method.In case that a low temperature plasma is used in the plasma CVD method,the temperature upon forming the DLC film can be set relatively low.Therefore, the low temperature plasma is suitable in case that anarticle having a low thermal resistance such as plastic is used as asubstrate, and furthermore, the low temperature plasma enables the DLCfilm to be formed on a wide area at a relatively low cost.

The low temperature plasma is a plasma in the non-equilibrium state inwhich electron temperature is high in the plasma and temperatures of ionand neutral molecule are remarkably low in comparison with thetemperature of the electron in case that the interior of the reactionchamber is maintained at a low pressure.

When the plasma is generated between the external electrode 12 and theinternal electrode 16, electrons are accumulated on the inner surface ofthe insulated external electrode 12 to electrify negatively the externalelectrode 12, namely, to generate negative self-bias on the externalelectrode 12. At the external electrode 12, a voltage drop occurs at arange from 500 to 1,000V because of the accumulated electrons. At thistime, carbon dioxide as the carbon resource exists in the plasma, andpositively ionized carbon resource gas is selectively collided with theinner surface of the container 20 which is disposed along the externalelectrode 12, and, then, carbons close to each other are bonded togetherthereby to form hard carbon film comprising remarkably dense DLC film onthe inner surface of the container 20. The hard carbon film of the DLCfilm is also called as i-carbon film or hydrogenated amorphous carbonfilm (a-C:H) and is an amorphous carbon film including mainly SP³ bond.

The thickness of DLC film is varied by an output of high frequency, apressure of the raw gas in the container 20, a gas flow rate forfeeding, period of time during which plasma is generated, self-bias andkind of raw material and the like. However, the thickness of DLC film ispreferably within a range from 0.05 to 5 μm to obtain the effectivesuppression of the sorption of the low molecular organic compound andthe improved gas barrier property, in addition to an excellent adhesionto plastic, a good durability and a good transparency. Quality of theDLC film is varied by output of the high frequency, the pressure of theraw gas in the container 20, the gas flow rate, the period of timeduring which plasma is generated, the self-bias and the kind of rawmaterial in the same manner. Increase of the output of high frequency,decrease of the pressure of the raw gas in the container 20, decrease ofthe flow rate of the supplied gas, increase of the self-bias, decreaseof the carbon number of the raw material and the like cause hardening ofthe DLC film, increase of the density thereof, increase of thecompressive stress thereof and increase of the fragility thereof.Therefore, in order to obtain the maximum sorption suppressing effect tolow molecular organic compound and the maximum gas barrier effect whilemaintaining an excellent adhesion and durability, it is preferable thatthe output of high frequency is set within a range from 50 to 1,000 W,the pressure of raw gas in the container 20 is set within a range from0.2 to 0.01 torr, the flow rate of supplied gas is set within a rangefrom 10 to 50 ml/min, the self-bias is set within a range from −200 to−1,000V, and the carbon number is set within a range from 1 to 8.

In order to enhance adhesion between the DLC film and the plasticmaterial, the inner surface of the container 20 may be activated byplasma treatment with inorganic gas such as argon and oxygen before DLCfilm is formed.

FIG. 4 shows a longitudinal section of plastic container on which theDLC film is formed in the above manner. In FIG. 4, numeral numbers 20 aand 20 b show a plastic material and a DLC film formed on the innersurface of the plastic material 20 a, respectively. In this manner, theplastic container whose inner surface is coated with the DLC film 20 bcan remarkably decrease permeability of low molecular inorganic gas suchas oxygen and carbon dioxide, and simultaneously can completely suppressthe sorption of various low molecular organic compounds having odor.Formation of the DLC film does not deteriorate transparency of theplastic container.

The following resins are used as plastic materials for containers 20:polyethylene resin, polypropylene resin, polystyrene resin, cycloolefinecopolymer resin, polyethylene terephthalate resin, polyethylenenaphthalate resin, ethylene-(vinyl alcohol) copolymer resin,poly-4-methylpentene-1 resin, poly (methyl methacrylate) resin,acrylonitrile resin, polyvinyl chloride resin, polyvinylidene chlorideresin, styrene-acrylonitrile resin, acrylonitrile-butadien-styreneresin, polyamide resin, polyamideimide resin, polyacetal resin,polycarbonate resin, polybutylene terephthalate resin, ionomer resin,polysulfone resin, polytetra fluoroethylene resin and the like.

With respect to the container coated with carbon film manufactured bythe above manufacturing apparatus and method, (1) Thickness of DLC film,(2) Density of DLC film, (3) Adhesion 1, (4) Adhesion 2, (5) Alkaliresistance, (6) Carbon dioxide gas barrier property, (7) Oxygen gasbarrier property and (8) Sorption of low molecular organic compound(aroma component) were evaluated in the following manners. The resultswere as follows:

(1) Thickness of DLC Film

Masking was previously made by Magic Marker (trade mark) on the innersurface of the container, and the DLC film was then formed. Thereafter,the masking was removed by diethyl ether, and thickness of the DLC filmwas measured by a surface shape measuring device (DECTACK 3) made byVecco Company.

(2) Density of DLC Film

Difference in weight between containers without the DLC film and withthe DLC film was measured, and the density of DLC film was calculatedwith the use of the thickness of the DLC film obtained in item (1).

(3) Adhesion 1

Adhesion of the DLC film formed on the side surface of the container wasmeasured in accordance with cross-cut tape test (JIS K 5400) under thefollowing conditions.

1. Distance between scratches: 1 mm

2. Number of checkers (lattices): 100

(4) Adhesion 2

Adhesion of the DLC film formed on the side surface of the container wasmeasured by a continuously weighting type scratch tester (HEIDON 22)made by SHINTO KAGAKU company under the following conditions. Degree ofadhesion was indicated by normal load exerted on a scratching needlewhen the film was started to be peeled off.

1. Material and shape of the scratching needle: diamond, 50 μR

2. Rate of loading: 100 g/min

3. Table speed: 1,000 mm/min

(5) Alkali Resistance

Alkali solution including sodium hydroxide of 10 wt % was filled intothe container which was then immersed in a water bath at a temperatureof 75° C. for 24 hours. Then, change of shape of the DLC film andexistence of peeling of the DLC film were investigated. “Excellence” inthe table shows that shape of DLC film was not changed and peelingthereof did not occur after the immersion for over 24 hours.

(6) Carbon Dioxide Barrier Property

Volume of carbon dioxide permeating the DLC film was measured by a PERMATRANC-4 type machine made by MODERN CONTROL Company at a temperature of25° C.

(7) Oxygen gas Barrier Property

Volume of oxygen permeating the DLC film was measured by an OXTRANTWINmachine made by MODERN CONTROL Company at a temperature of 40° C.

(8) Sorption of Low Molecular Organic Compound (Aroma Component)

Low molecular organic compound (aroma component) having odor was used asa kind of environmental material to test the sorption with reference toa method by MATSUI et al. (J. Agri. Food. Chem., 1992, 40, 1902-1905) inthe following manner.

1. Model-flavor solution was prepared in such a manner that each aromacomponent (n-octane, n-octanal, n-octanol, ethyl hexanoate, andd-limonene) of 100 ppm was added to sugar ester solution to obtain 0.3%sugar ester solution.

2. The model flavor solution of 700 ml was poured into the container,the container was left at a temperature of 20° C. for one month afterthe mouth of the container was closed with the cover.

3. One month later, the model flavor solution was removed from thecontainer to dry the interior of the container after the interiorthereof was washed with distilled water of 60° C.

4. Diethyl ether was poured into the container to extract aromacomponent sorbed in the container.

5. The diethyl ether was taken out of the container to dehydrate thediethyl ether by adding sodium sulfuric anhydride thereto.

6. Quantitative analysis was performed by the gas chromatography inwhich amylbenzene was used as internal standard. In case that solutionincluding aroma component of 1 ppm exists in the container, amount ofthe aroma component sorbed in the container is indicated by μg.Therefore, unit is μg/ppm/bottle.

[Test 1]

A plastic container having a volume of 700 ml and made of polyethyleneterephthalate resin (PET resin, Type L125 made by MITSUI PET RESINCOMPANY LIMITED) was accommodated in the external electrode 12 as shownin FIG. 1 to be fixed thereto.

Then, the vacuum pump was operated to make the inside of the externalelectrode 12 vacuum (back pressure) of lower than 10⁻⁴ torr, and,thereafter, for preliminary treatment, argon was supplied into theplastic container at a flow rate of 30 ml/min to obtain a pressure of0.04 torr in the container, and Rf power of 300W was supplied to performplasma treatment on the inner surface of the container. Thereafter, rawgas such as toluene, cyclohexane, benzene or p-xylene was supplied intothe interior of the container with using argon as auxiliary gas touniformly form the DLC film on the inner surface of the container underthe conditions shown in FIG. 5.

Result of Test

FIG. 6 shows the results of the evaluation with respect to thickness offilm, film forming velocity, density of film, adhesion 1 of film,adhesion 2 of film and alkali resistance of film. The density of eachfilm exceeded 2.00 g/cm³, and the formed film was remarkably dense.

According to the cross-cut test, the adhesion to polyethyleneterephthalate resin was good, and it was verified that the container wassufficient to be of practical use. Furthermore, it was found that alkaliresistance was good, and the DLC film was stable enough to completelyprotect the polyethylene terephthalate resin.

The results of oxygen permeability, carbon dioxide permeability anddegree of the sorption of each aroma component are shown in FIG. 7.Dense DLC film completely suppressed the sorption of aroma component,and simultaneously, effectively suppressed permeation of oxygen andcarbon dioxide.

In addition, FIG. 8 shows the transmitted light spectrum in ultravioletand visible region at the barrel portion of the plastic container, theinner surface of which was coated with the DLC film.

Light transmittance rate was abruptly decreased in a region fromapproximately 500 nm of wave length to the ultraviolet region. Thissuggests that the coating with the use of the DLC film is effectiveenough to suppress the deterioration of contents by ultraviolet.

FIG. 9 shows Raman spectrum of the thin film formed on the barrelportion of the plastic container under the conditions of Test 1.

[Test 2]

The DLC film was formed on the inner surface of the container in thesame manner as Test 1 except that a plastic container, having a volumeof 700 ml made of styrene-aecrylonitrile copolymer resin (made byMitsubishi Monsant Kasei Company: PAN resin, type L700) was used. Theconditions for forming the DLC film are shown in FIG. 10. In the samemanner as Test 1, tests were performed in connection with the DLC film,namely, thickness, density, adhesion 1, adhesion 2, alkali resistance,carbon dioxide barrier property, oxygen gas barrier property andsorption of low molecular organic compound.

Result of Test

The results of the test in connection with the DLC film, namely,thickness of film, film forming velocity, density of film, adhesion 1 offilm, adhesion 2 of film and alkali resistance of film were shown inFIG. 11. The thickness of the film and the density thereof were good inthe same way as Test 1. It was found that the adhesions 1 and 2 weregood in the same way as Test 1 and the adhesion between the DLC film andthe styrene-acrylonitrile copolymer was of practical use in the same wayas that between DLC film and polyethylene terephthalate resin.

FIG. 12 shows oxygen permeability, carbon dioxide permeability anddegree of sorption of each aroma component. More specifically, it wasfound that styrene-acrylonitrile copolymer resin was inherentlyexcellent in gas barrier property, and further, the permeating amount ofeach of oxygen and carbon dioxide with respect to styrene-acrylonitrilecopolymer resin was remarkably decreased to an extremely lower level bythe formation of the DLC film. Amount of the sorption of each aromacomponent was smaller than the detectable limit, and there was noproblem in sensory test in the same way as Test 1.

[Test 3]

The DLC film was formed on the inner surface of the container in thesame manner as Test 1 except that a plastic container having a volume of700 ml made of cycloolefine copolymer resin (made by MITSUIPETROCHEMICAL COMPANY LIMITED: COC resin, type APL 6015) was used. Theconditions for forming the DLC film are shown in FIG. 13. In the samemanner as Test 1, tests were performed in connection with the DLC film,namely, thickness of film, density of film, adhesion 1 of film, adhesion2 of film, alkali resistance of film, carbon dioxide barrier property offilm, oxygen gas barrier property of film and sorption of film to lowmolecular organic compound.

Result of Test

The results of each test in connection with the DLC film, namely,thickness of film, film forming velocity, density of film, adhesion 1 offilm, adhesion 2 of film, alkali resistance of film are shown in FIG.14. In the same manner as Tests 1 and 2, there was no problem withrespect to all testing items, and, in particular, the adhesion betweenthe DLC film and the plastic container was remarkably excellent.

FIG. 15 shows results of the oxygen permeability of the DLC film, thecarbon dioxide permeability thereof and the sorption of each aromacomponent. Cycloolefine copolymer resin has comparatively large oxygenpermeability carbon dioxide permeability and sorption of aromacomponents because it is olefine type resin. However, it was found thatthe formation of the DLC film on the container could considerablysuppress the oxygen permeability, the carbon dioxide permeability andthe sorption of aroma components.

INDUSTRIAL APPLICABILITY

The plastic container coated with carbon film of the invention can beused as a returnable container such as a bottle for beer, sake as wellas beverage.

What is claimed is:
 1. A method of recycling a container, the methodcomprising washing the container, and filling the washed container witha substance, wherein the container comprises an outer shell comprising aplastic, and a diamond-like carbon film bonded to an inside surface ofthe outer shell; and the diamond-like carbon film restrains adsorptionby the container of an aroma component, which comprises low molecularorganic compounds, to below a detectable limit.
 2. The method of claim1, wherein the container is a bottle used for beverages.
 3. The methodof claim 1, further comprising forming the diamond-like carbon film by aprocess comprising disposing an external electrode outside thecontainer; disposing an internal electrode inside the container, wherethe internal electrode supplies a gas to the inside of the container;and forming the diamond-like carbon film by plasma chemical vapordeposition.
 4. The method of claim 1, further comprising forming thediamond-like carbon film by a process comprising placing a containerenclosing a hollow space and having an inner and outer surface into ahallow space of an external electrode having an internal surfaceconforming in shape to the outside surface of the container; providingfor a vacuum between the internal surface of the external electrode andthe outer surface of the container, all of the outer surface of thecontainer being positioned at an about equal distance from the internalsurface of the external electrode; inserting an internal earthedelectrode into the hollow space of the container; providing a vacuum inthe hollow space enclosed by the container; introducing a gas of aprecursor for forming the diamond-like carbon film into the hallow spaceenclosed by the container; applying an AC voltage to the externalelectrode; and forming the diamond-like carbon film.
 5. The method ofclaim 1, further comprising forming the diamond-like carbon film by aprocess comprising preparing an external electrode having a hollow spacesubstantially similar to an external shape of the container and aninternal grounded electrode having an external shape substantiallysimilar to an internal shape of the container; placing the container inthe hollow space of the external electrode in such a manner than adistance between the bottle and the external electrode is keptapproximately even at every position of the container; inserting theinternal electrode into the container in such a manner that a distancebetween the internal electrode and the container is kept approximatelyeven at every position of the bottle; providing a vacuum within a rangeof 10⁻² to 10⁻⁵ torr in the hollow space of the external electrode;introducing a gas of a precursor for forming the diamond-like carbonfilm into the container; applying an AC voltage with an output of 50 to1000 W to the external electrode; and forming the diamond-like carbonfilm.
 6. The method of claim 1, wherein the diamond-like carbon film isfrom 0.05 to 5 μm thick.
 7. The method of claim 1, wherein the plasticcomprises at least one member selected from the group consisting ofpolyethylene resin, polypropylene resin, polystyrene resin, cycloolefincopolymer resin, polyethylene terephthalate resin, polyethylenenaphthalate resin, ethylene-(vinyl alcohol) copolymer resin,poly-4-methylpentene-1 resin, poly(methylmethacrylate) resin,acrylonitrile resin, polyvinyl chloride resin, polyvinylidene chlorideresin, styrene-acrylonitrile resin, acrylonitrile-butadiene-styreneresin, polyamide resin, polyamideimide resin, polyacetal resin,polycarbonate resin, polybutylene terephthalate resin, ionomer resin,polysulfone resin and polytetrafluoroethylene resin.
 8. The method ofclaim 1, wherein the plastic is selected from the group consisting of apolyethylene terephthalate resin and a styrene-acrylonitle copolymerresin; the diamond-like carbon film has a density greater than 2.00g/cm³; and a permeating amount of oxygen in a day per a bottle capacityof one liter is less than 12.7 micro-liters.
 9. The method of claim 1,wherein the plastic comprises polyethylene terephthalate resin; and thediamond-like carbon film has a density less than or equal to 2.84 g/cm³.10. The method of claim 1, wherein the plastic comprisesstyrene-acrylonitrile copolymer resin; and the diamond-like carbon filmhas a density less than or equal to 2.94 g/cm³.
 11. The method of claim1, wherein the aroma component comprises d-limonene; and thediamond-like carbon film restrains sorption of the d-limonene by thecontainer to substantially zero.
 12. A method of recycling a container,the method comprising washing the container, and filling the washedcontainer with a substance, wherein the container comprises an outershell comprising a plastic, and a diamond-like carbon film bonded to aninside surface of the outer shell; and the diamond-like carbon filmrestrains adsorption by the container of an aroma component, whichcomprises low molecular organic compounds, to effectively zero.